In 3GPP (3rd Generation Partnership Project), has been examined evolution of a radio access system and a radio network of cellular mobile communication (hereinafter referred to as “LTE (Long Term Evolution)” or “EUTRA (Evolved Universal Terrestrial Radio Access)”). In the LTE, an OFDM (Orthogonal Frequency Division Multiplexing) system, which is multicarrier transmission, is used as a communication system for wireless communication from a base station apparatus to a mobile station apparatus (downlink). In addition, an SC-FDMA (Single-Carrier Frequency Division Multiple Access) system, which is single career transmission, is used as a communication system for wireless communication from the mobile station apparatus to the base station apparatus (uplink).
In the LTE, the base station apparatus decides radio resource assignment, a coding rate, a modulation scheme, etc. of a PUSCH (Physical Uplink Shared Channel), which is the channel for data transmission transmitted by the mobile station apparatus and of a PDSCH (Physical Downlink Shared Channel), which is the channel for data transmission transmitted by the base station apparatus. In addition, the base station apparatus transmits DCI (Downlink Control Information) indicating the radio resource assignment to the mobile station apparatus using a PDCCH (Physical Downlink Control Channel).
Hereinafter, the PDCCH will be described in more detail. The PDCCH is allocated in one or more CCEs (Control Channel Elements). The CCE is a unit of a radio resource in which the PDCCH is allocated. In addition, a common search space and a user equipment-specific search space are comprised of the plurality of CCEs.
The common search space is the space common among the plurality of mobile station apparatuses, and is the space where the PDCCH for the plurality of mobile station apparatuses and/or the PDCCH for a specific mobile station apparatus are allocated. The common search space is comprised of a predetermined CCE. The user equipment-specific search space is the space where the PDCCH for the specific mobile station apparatus is allocated, and is the space configured for each mobile station apparatus. As for the common search space and the user equipment-specific search space, different common search space and user equipment-specific search space are configured for each number of the CCEs in which the PDCCH is allocated. Note that a part or all of the common search space and the user equipment-specific search space may overlap with each other, a part or all of the different common search spaces may overlap with each other, a part or all of the different user equipment-specific search spaces for the same mobile station apparatus may overlap with each other, and that a part or all of the user equipment-specific search spaces for the different mobile station apparatuses may overlap with each other.
A plurality of formats is prepared for DCI transmitted by the PDCCH. A format of the DCI is called a DCI format. In the DCI formats, there are included a DCI format with a same bit number (or also referred to as a “payload size”) as the other DCI formats, and a DCI format with a different bit number from the other DCI formats. The base station apparatus adds to the DCI a sequence in which a CRC (Cyclic Redundancy Check) code generated based on the DCI is scrambled (or referred to as masked) by RNTI (Radio Network Temporary Identity).
The mobile station apparatus changes an interpretation of the DCI depending on by which RNTI the CRC code is scrambled. Hereinafter, a state where the CRC code scrambled by the RNTI has been added to the DCI will be represented simply as that the RNTI is included in the DCI, or the RNTI is included in the PDCCH. For example, the mobile station apparatus discriminates a type of the DCI format of the DCI from the RNTI included in the DCI.
The base station apparatus encodes the DCI according to the bit number of the CCE, and allocates it in the common search space or the user equipment-specific search space. Note that the base station apparatus performs the same coding of DCI formats with a same bit number, and that performs different coding of DCI formats with different bit numbers. Namely, since a coding scheme which the base station apparatus applies to the DCI format differs depending on the bit number of the DCI format, a decoding method of the DCI format in the mobile station apparatus differs depending on the bit number of the DCI format. Accordingly, the mobile station apparatus can discriminate the type of the DCI format based on a difference of the bit number of the DCI format, or of the decoding method. When the bit number of the DCI format is the same as each other, the mobile station apparatus is made to be able to discriminate the type of the DCI format by using a method for including in the DCI format information for discriminating the type of the DCI format, or for adding a CRC code scrambled by RNTI corresponding to the type of the DCI format, etc.
When the mobile station apparatus performs decoding processing of all the CCE candidates in which the PDCCH is allocated in the common search space and the user equipment-specific search space, further descrambles by the RNTI a sequence in which the CRC code has been scrambled by the RNTI, and detects no error in the descrambled CRC code, it determines to have succeeded in obtaining the PDCCH. This processing is called blind decoding.
In addition, in the 3GPP, has been examined a radio access system and a radio network that achieves higher-speed data communication (hereinafter referred to as “LTE-A (Long Term Evolution-Advanced)” or “A-EUTRA (Advanced Evolved Universal Terrestrial Radio Access)”) utilizing a wider frequency band than the LTE. It is required that the LTE-A has backward compatibility with the LTE, i.e., a base station apparatus of the LTE-A simultaneously performs wireless communication with mobile station apparatuses of both the LTE-A and the LTE, and the mobile station apparatus of the LTE-A can perform wireless communication with base station apparatuses of both the LTE-A and the LTE, and it has been examined that a same channel structure as in the LTE is used for the LTE-A.
In the LTE-A, has been examined a technology (frequency band aggregation, also referred to as spectrum aggregation, carrier aggregation, frequency aggregation, etc.) in which a plurality of frequency bands (hereinafter referred to as “CCs (Component Carriers)”) with the same channel structure as in the LTE are used as one frequency band (wide frequency band). Specifically, in communication using the frequency band aggregation, a downlink channel is transmitted for each downlink CC, and an uplink channel is transmitted for each uplink CC. Namely, frequency band aggregation is a technology in which a base station apparatus and a plurality of mobile station apparatuses simultaneously transmit and receive a plurality of data information and a plurality of control information using a plurality of carrier components including a plurality of channels in an uplink and a downlink.